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Abstract

In this work, a first report on fabricating an asymmetric Bragg coupler-based filter on polymeric waveguides without input-waveguide grating was revealed. The fabrication process we developed was using holographic interference techniques, capillary effect, soft lithography, and micro molding process. The transmission dip of about −9.2 dB and the 3 dB transmission bandwidth of about 0.125 nm were obtained from a filter.

Fabrication process of buried grating in polymeric waveguide filter structure:(a) A negative photoresist and UV polymer are deposited on the glass (b) The photoresist is exposed to the UV light through a photo mask (c) The asymmetric waveguide coupler mold (d) H-PDMS is injected into a waveguide of the photoresist mold (e) The positive photoresist is deposited on the mold (f) The grating is holographically exposed on the positive photoresist of the mold (g) The grating is patterned on an alternative waveguide of the mold (h) The PDMS is spun on the mold (i) The PDMS adhered with H-PDMS is removed to form a master mold (j) The master mold (k) The H-PDMS is injected into the grating-engraved waveguide (l) The PDMS is spun on the master mold to form a stamp (m) The PDMS adhered with H-PDMS is removed to obtain a stamp (n) The stamp mold (o) An ABC pattern is transferred from PDMS stamp to an Ormo-comp polymer (p) The Ormo-comp polymer is exposed to a wide band UV light (q) The PDMS stamp is removed (r) A hardened Ormo-comp polymer forms a cladding layer of the ABC filter (s) An Ormo-core polymer is injected into the channel to form the waveguide core (t) An Ormo-comp polymer is deposited (u) The Ormo-comp layer is cured by exposing the UV light to form the final filter.

Optical-microscope photograph of an asymmetric Bragg coupler mold; the positive photoresist filled into the wider waveguide groove; the final cross-sectional dimensions are 6.8 μm × 6 μm and 9.6 μm × 5 μm, and the gap is about 2.1 μm.

SEM micrograph of the UV epoxy groove showing the intact grating pattern inside the groove (the dimensions are 6.8 μm × 6 μm and 9.6 μm × 5 μm, the gap is about 2.4 μm, the grating length is about 15 mm, and the grating depth is about 450 nm.

Optical-micrograph of the output end of an ABC-based filter (a) the wider waveguide (cross-sectional dimension is 5 μm × 9.6 μm), and (b) the narrower waveguide (cross-sectional dimension is 6 μm × 6.8 μm). It shows that there is no unguided layer outside the core region.

Near field intensity distribution of two output waveguides: (a) the wide waveguide (with grating), (b) the narrow waveguide (without grating). The ASE laser with the power of 3 mW was shone onto the narrow waveguide.